The present invention relates to a heat setting chamber for the continuous heat setting of yarns, comprising entry and exit openings for transport belts which transport the yarns in loops, also comprising fans and flow guiding means for generating a circulation of superheated steam transversely to the transport direction of the yarns and directed at the loops. A feeder duct is provided for feeding steam, a heating system is provided for superheating the steam, extractor vents are provided for extracting a part of the steam arranged above the loops in the area of the entry and exit openings, and ventilation seals are provided underneath the loops in the area of the entry and exit openings, said ventilation seals being arranged inside the heat setting chamber and producing a counter-flow of steam directed against the loops.
A heat setting chamber of this general type is prior art in U.S. Pat. No. 4,513,514. In the case of the known heat setting chamber, socalled pre-zones are provided outside of the actual entry and exit openings and at which a part of the heat setting medium, in this case superheated steam, is extracted. The pre-zones are connected above the transport belts to exhaust steam vents, which extract upwards part of the steam circulating in the heat setting chamber. In the area of the pre-zones, but still inside the heat setting chamber, the steam, normally circulating from above, is re-routed in such a way that it circulates against the yarn loops from below in the so-called counter-flow principle, thus forming a ventilation seal. The result of this arrangement is that the lower area of the yarn loops practically only comes into contact with the superheated steam first inside the heat setting chamber, while in the upper area the yarn loops have already been heated by steam in the pre-zone. This results in the heat setting duration or the dwell time of the upper area of the loops being somewhat longer than for the lower area of the loops. The area of the loops which comes into contact with the heat setting medium first shrinks sooner than that area of the loops which comes into contact with the heat setting medium later. As the heating up of the upper area of the loops begins sooner, the loops reach the heat setting temperature sooner here than in their lower area. This can lead to a so-called marbled effect in finished fabric products, especially in carpets, which means that non-dyed yarns treated with superheated steam later color unevenly in the carpet. This is especially true for polyamid yarns. A further disadvantage in the known arrangement is that the superheated steam in the upper area of the loops is wetter than the steam which penetrates the lower area of the loops in the ventilation seal. This is because, as a result of extraction through the pre-zone, the superheated steam mixes a little with the cold air coming into the heat setting chamber and is thus cooled down. In the case of a very short heat setting chamber with a short dwell time, it can happen that the upper area of the yarn loops reaches a different heat setting temperature from the lower area of the yarn loops.
It is an object of the present invention to avoid the above mentioned disadvantages present in prior art, and to make a heat setting chamber in which the upper and lower areas of the yarn loops come into their first contact with the superheated steam simultaneously.
This object has been achieved in accordance with the present invention in that the mouths of the extractor vents are arranged essentially vertically over the ventilation seals and inside the heat setting chamber.
According to the present invention, the yarn loops first come into contact with the superheated steam only after they have fully entered the heat setting chamber, and then simultaneously in the upper and lower areas. In the lower areas the yarn loops are heated by the counter-flow of the ventilation seals, while a practically identical superheated steam is extracted vertically over the ventilation seals up through the upper area of the loops. This results in the yarn entering the heat setting chamber being shrunk or bulked simultaneously in all areas of the loops. Furthermore, all areas of the loops can reach the same heat setting temperature simultaneously. The same effect is achieved when the transport belts with the loops placed thereon are fed through the exit openings. Here all areas of the loops come into contact simultaneously with the superheated steam for the last time. It is further avoided that parts of the yarn loops come into contact with varying steam wetness.
It is advantageous that the mouths of the extractor vents extend essentially over the entire operational surface of the loops. This ensures that the steam flow of the ventilation seal is extracted in equal flow widths.
The cross section of the extractor vents can be advantageously varied by means of a cover plate according to certain preferred embodiments of the invention. The intensity of the extraction can thus be adapted to the intensity of the counter-flow of the ventilation seal.
In certain preferred embodiments of the invention, in the area of the ventilation seals, additional ventilation flows can be directed laterally against the loops. Thus the loops are not just penetrated with superheated steam in their upper and lower areas, but also sideways.
For the purpose of the present invention, the extractor vents are connected to an extractor channel which extends transversely outside of the heat setting chamber, and has a smooth, uninsulated floor surface arranged above the entry and exit openings. If the floor of the extractor channel is not insulated the floor surface can heat up to over 120.degree. C. due to the high temperature of the exhaust steam, so that no condensation can form at this point.
As desired, suction mouths, disposed on the floor surface and arranged at both the entry and exit openings, can be additionally provided according to preferred embodiments. These additional suction mouths, which are superfluous in most cases, can take up the rest of the exhaust steam which is not extracted by the extractor vents. Thus a small amount of exhaust steam passes out through the entry and exit openings and into the extractor channel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.